Electrostatic clutches



Sept. 26, 1967 1 A, DONELAN ET AL 3,343,636

ELECTROSTATIC CLUTCHES Filed Dec. '7, 1965 2 Sheets-Sheet 1 BY @MMQL di? FITTRNWS Sept. 26, 1967 A DONELAN ETAL 3,343,636

' ELECTROSTATIC CLUTGHES Filed Dec. 7, 1965 2 Sheets-Sheet 2 Fig. s

INVENTURS I JPM/165 n, DOVEUA/ HTTUQNSY United States Patent Office iddii Patented Sept. 26, i967 3,343,636 ELECROSTA'HC CLUTCHES Eames A. Donelan, West Harrow, and Howard H. W. Losty, Watford, England, assignors to The General Electric Company Limited, London, Engiand, a British company Filed Dec. 7, 1965, Ser. No. Si2,064 Claims priority, application Great Britain, Dec. 8, 1964, 49,35/64 9 Claims. (Cl. 192-84) ABSTRACT F THE DISCLOSURE An electrostatic clutch of the lohnsen-Rahbek type having two mutually engageable components which can experience relative movement when disengaged and no relative movement when engaged, the engageable surfaces of the components being in slipping contact when the components are disengaged and experiencing relative motion, one of the components having an engageable surface member formed by a plurality of separate sections, each individually mounted by a ball bearing on the body of that component so as to be capable of universal pivotal movement relative to said body.

rl`his invention relates to electrostatic clutches of the kind (hereinafter referred to as the kind specied) depending upon the Johnsen-Rahbek edect for their operation.

The Iohnsen-Rahbek effect is the production of an electrostatic attraction, known as the Johnsen-Rahbek force, between a surface of an electrically conducting member and a closely adjacent surface of a semiconductive member, under the application of a voltage between the said members. When the said surfaces are initially in such close juxtaposition that they are in slipping contact, the lohnsen-Rahbek force produced between them when the voltage is applied is capable of causing adhesion between the surfaces, provided that the applied voltage is suflciently high to produce a Johnsen- Rahbek force of the requisite magnitude. This effect, and its application in effecting engagement between two components of an electrostatic clutch, are described by A. D. Stuckes in an article entitled, Some Theoretical and Practical Considerations of the lohnsen-Rahbek Eect, published in the Proceedings of the Institution of Electrical Engineers, volume 103 (B), 1956, pages 125 to 131.

The term clutch as employed herein is to lbe understood to mean a device comprising two mutually engageable components between which there may be relative movement when disengaged but substantially no relative movement when engaged. Thus a clutch may consist of a driving component and a driven component to which the motion of the driving component is imparted on engagement of the two components, or of a stationary component and a movable component the motion of which is stopped on engagement with the stationary cornponent, the latter arrangement thus performing the function of a brake. In the case of an electrostatic clutch, the components are arranged to be in slipping contact when disengaged and in relative motion.

The invention is especially, although not exclusively, concerned with electrostatic clutches of the kind specified which are of the type comprising a rotatable driving component and a driven component, engageable therewith, which is caused to rotate at substantially the same speed when fully engaged with the driving component. For example, each of the clutch components may be a disc or cylinder, the mutually engageable surfaces of the cornponents (the end face in the case of a cylinder) being in general substantially perpendicular to the axis of rotation which is common to both components, the said surfaces being so shaped as to conform closely to one another and vbeing in slipping contact when not engaged. One component of the clutch comprises a semiconductive member consisting of a surface layer of semiconductive material, which provides the engageable surface of the component and which is in contact either with a metal body forming the main part of the said component or with an electrically conducting layer interposed between the semiconductive layer and the main body of the component if the latter is of insulating material. The second component of the clutch may be formed wholly of metal or may include a metal member forming the engageable surface. It is immaterial, from the point of view of the production of the Johnsen-Rahbek effect, whether the semiconductive layer is provided on the driving component or on the driven component.

The term engageable surface is used herein to refer to that surface of a clutch component which is arranged, in operation of the clutch, to engage with a surface of the other component of the clutch, and the term engageable surface member means an electrically conducting or semiconductive layer or member a surface of which provides such an engageable surface.

The electrically conducting parts of the clutch components, that is to say the metal engageable surface member of one component and the metal body or layer in contact with the semiconductive engageable surface member of the other component, are arranged to be connected to a source of electric current supply for the application of the required voltage between the said surface members of the components, for effecting operation of the clutch.

It is an object of the present invention to provide an improved construction of an electrostatic clutch of the kind specilied.

According to the invention, in an electrostatic clutch of the kind specified and comprising two mutually engageable components between which there may be relative movement when disengaged and substantially no relative movement when engaged, and the engageable surfaces of which are in slipping contact when disengaged and in relative motion, the engageable surface member, as hereinbefore defined, of one of the clutch components is formed in a plurality of separate sections each individually mounted on a surface of the main body of said component so as to be capable of pivotal movement, relative to said main body, such that the engageable surface of each of said sections is individually alignable with the engageable surface of the second component of the clutch when the two components are in the disengaged position.

Preferably each of said individual engageable surface member sections is mounted so as to be capable of universal pivotal movement relative to the main body of the clutch component of which they form part.

The ability of the engageable surface sections of one component of the clutch to be aligned individually with the engageable surface of the other component will in general enable closer interfacial contact to be obtained between the two engageable surfaces as a whole, when they are in slipping contact, than if both said surfaces are included in single, integral, surface members. This improved interfacial contact ensures that, on the application of a voltage between the engageable surface members, the Johnsen-Rahbek force produced is rapidly effective to cause the said surfaces to engage, so that a clutch in accordance with the invention is advantageous in that it is capable of high speed operation. The improved interfacial contact between the clutch components also results in a reduction in the amount of slip occurring be-V tweenthe surfaces when they are engaged. The term slip is applied to the relative difference in speed of move-V ment between the two components of the clutch: kwhen the components are engaged the slip is only slight, being observable by stroboscopicmethods, and is expressed as slip angle per revolution Vin the case of a clutch comprising rotating driving and driven components. The above input means for connection to'the supply. The clutch ofV Ythe invention is, however, particularly Ysuitable for opera- Y tion from a polyphase supply, since the individual surstatement that there is substantially no relative move- Y ment between the clutch'components when engaged is intended torreferV to theV possible slight amountof slip between them.

The invention will be yfurther described mainlyV with 'reference to rotating clutches, that'is to sayclutches of the type comprising a driving component and a driven V,component which are rotatable about a common axis.

A number of other advantages can be obtained with a clutch construction in accordance with the invention: thus we have found that an increase in the torque transmitted in operation of Va rotating clutch can be obtained,

Y for a given clutch Vsize and power input, as compared with that obtained with the conventional disc clutch construction comprising two single discs engageable with one another. We have also found that suitable drive conditions for a clutch according to the invention are easily Y obtained, and that, provided that the frictional drag between the clutch components is relatively low, for ex- Y VampleV about?. lbs. inch, prolonged periods of slipping between operationsrof the clutch do not result in appreciable Wear of the surfaces or have any deleterious effect on the performance of the clutch. Furthermore, great accuracy of alignment between the engageable surfaces as Ya whole, jand of the finish of the surfaces, in'manufacture of the VYcomponents of a clutch in accordance with the invention, are'not necessary, with resulting easement of manufacturing tolerances. v Y

The individually mountedrsurfacesections may constitute the engageable member of either the driving component or the driven component of a rotating clutch, and Ymay be formed either of a suitable metal for forming the electrically conducting surface,'or of a suitable semiconfstitute'the metal surface member, they may be, and for ,some modes of operation are (as will appear later), mounted on an insulating body which may form, or may be supported by, the main body of the clutch component concerned, and suitable conductors are then provided on or within the saidcomponent' for connecting the said sections to an electric current supply for operation of the clutch. lf the said individual sections constitute the semiconductive surface member, each section is'supported on, ,or attached to,'a metal member or layer, such metal members or layers being in close contact with the re- Y Vspective sections of semiconductive material. These metal members or layers similarly may be, and for some modes of operation are, insulated from one another, and are then arranged to be connected to an electric current supply by means of suitable conductors providedvon -or within therbody of the clutch component.

An electrostatic clutch according to the invention can be operated either from a direct current supply, or from a single phase or polyphase alternating current supply. For direct current or single phase alternating current operation, the individually mounted surface sections Yconstituting the engageable surface member of one of the clutch components will be arranged to haveV a common ation and sixrse'ctions for Vthree-phase operationidf deff material.

face sections can conveniently be'arranged to be Vseparately connected to the respective'supply conductors fromV the different phase circuits. Thus in aV preferred method'.VY`V` 1of operating a clutch in accordance with the invention, the

individually mounted surface sections of one componentV are arranged to be connected separately to the respective 't phase line conductors of a star-connected polyphase alternating current system, at least one said section beingy provided for connection to each phase circuit, and the single engageable surfaceV member of the other clutch component is arranged to be connected to the neutral conductor of the polyphase system, if desired. Connection of the second component to the neutral conductor of Va balanced polyphase system is, however, Vnot essential.

Furthermore in a clutch whichV is to be operated from aV balanced polyphase system, it will be necessary to ensure f that the said individually mounted surface sections all possess the same electrical impedance. This is conveniently achieved by forming all said sections of the same dimensions. Y Y

For polyphase operationrof a rotating clutch, prefer ably a pair of the said individually mountedV surface sections is provided for connection to each phase circuit, the sections of reach pair preferablyV being located diametrically opposite to toneV another on Ythe face of the appropriate clutch component. Thus, for example,

four such sections may be provided for two-'phase Vopersired, more than'two said sections may be provided for Y connection to each phase circuit, Ythesections Yto belcon-V nected to any one phase preferably being symmetrically spaced apart upon the faceL of theeclutch component.

The required mobility of the engageable surface member sections can be achieved by mounting the individual sections on ball bearings, which are suitably supported in apertures or recesses in the body gof the clutch f component. Preferably each such ball .bearingV is supported on one end of a compression spring, which is retained in a chamber Within the component body. Electrical connections can then be conveniently made from each surface section, through the appropriate ball bearing and spring, to a'conductor carried on the component,V for example a slip-ring, for connection Vto the supply Y when the body of the clutch component is of insulating Usually, in a clutch of the type comprisingrtwo substantially cylindrical components, the mutually engageable surfaces of the components are the substantially plane end surfaces; in a clutch of this type in accordance with the present invention, the individually'mounted surface sections of one component, and'theengageable surface member of the otherrcomponent, will usually have substantially .plane engageable surfaces. gHowever,

the mutually engageable surfaces need not necessarily be Y plane, but may be of anydesired conformation, provided thateach said individual surface section is of such a shape that its engageable'surface conforms closely to that portion of the surface of the other clutch coinponent with which it is arranged to engage in .operation of the clutch. Y Y

Therengageable` surfaces of the individually alignable surface sectionsr'may be circular, the sections of the revelant engageable surface member being in the form of discs. In some cases, however, for obtaining higher values of the torque transmitted in operation of a rotating clutch, the engageable surface area of each section is made as large as possible, the sections being so. shaped and arranged on the face of the .main body of the clutch componentV on which they'are mounted that theyoccupy nearly the whole of the Vsaid face of the main body, with only small insulating spaces between the sections. Thus in one preferred arrangement, Where the said clutch component is a cylinder or disc and the engageable surface member sections are mounted on a circular end face of the main body of the component, the said sections are each in the form of a sector of a circle and are arranged so that the arcs of the sectors lie close to, and substantially parallel to, the perimeter of the face of the main body, the narrow ends of the sectors enclosed by the two radii, which ends may be angled, truncated, or curved, extending towards the centre of the said face of the main body.

The semiconductive material employed for the construction of either the individually mounted surface sections, or the single engageable surface member of the other clutch component, as the case may be, can be any semiconductive material known to be suitable for use in electrostatic clutches employing the Iohnsen-Rahbek effect, such as some ceramic dielectric materials. However, the preferred material for use for the semiconductive surface member or sections, in a clutch in accordance with the invention, is semiconductive carbon preferably composed of partially carbonised regenerated cellulosic or hemicellulosic material, which is advantageous for use in electrostatic clutches since it possesses self-lubricating properties, and also possesses electrical resistivity in a range of suitable values, is hard and machinable and can be polished to give a satisfactory surface iinish, and has suitable friction characteristics and thermal conductivity, the electrical, frictional and thermal properties being adjustable as desired by control of the process of manufacture of the carbon. In addition, when this semiconductive carbon is employed for the individually mounted surface sections, as is preferred, in a clutch in accordance with the invention, the asperities present on the carbon surface are considerably worn down during the initial periods of slipping between the clutch components, due to a polishing action of the metal surface in slipping contact with the carbon surface. This adjustment of the carbon surface results in a marked increase in the torque available, and lreduction of the slip angle, in operation of a rotating clutch, as compared with the torque and slip angle characterising the clutch when it is rst assembled. Furthermore this polishing action results in an increase of the true area of contact, a decrease in the effective width of the air gap, and an increase in the electric I'ield, between the engageable surfaces of the clutch components during slipping; on engagement of the surfaces, the high electric eld causes etching of the carbon surfaces, which in turn results in a decrease in the electric eld: thus in a clutch in accordance with the invention, with individually alignable surface sections composed of semiconductive carbon of the kind referred to, the micro-roughness of the carbon surface is self-adjustable, in operation, to maintain the electric field between the engageable surfaces substantially constant,

A specific form of clutch in accordance with the invention, and an arrangement comprising a combination of two clutches according to the invention, will now be described by way of example, with reference to the accompanying drawings, in which:

FIGURE l is a perspective view of the two components of a clutch of the form comprising a driving component and a driven component both rotatable about a common axis;

FIGURE 2 is a part-sectional side elevation of the driving component of the clutch shown in FIGURE l;

FIGURE 3 is a front elevation of a modified form of the engageable surface of the driving component of a clutch similar to that shown in FIGURES l and 2; and

FIGURE 4 is a diagrammatic part-sectional elevation of an arrangement comprising a combination of a clutch mechanism and a brake mechanism, both constructed in accordance with the invention.

In the drawings, like parts are indicated by the same reference numerals in the respective gures.

Referring to FIGURES l and 2 or the drawings, the driving component of the clutch comprises a cylindrical main body, 31, of high strength insulating material, for example a high strength synthetic resin, carried on a mild steel hub 32, the extension of which, 33, is arranged to mate onto the output shaft of the power source employed to drive the clutch (the said power source is not shown in the drawing). On the end face 34 of the insulating body 31 are mounted six discs of semiconductive carbon, 35, all of the same dimensions and equally spaced around the periphery of the face 34, being located in recesses 36. Each carbon disc is backed with a coating of silver, 37, and is mounted in an aluminum cup 38, the silver-coated surface of the carbon disc being iixed to the interior surface of the aluminum cup by means of an adhesive resin containing a dispersion of silver flake. A steel ball 39 is fixed to the centre of the outer surface of each of the aluminum cups: this ball serves to locate the aluminum cup and carbon disc centrally with respect to the open end of a chamber, 40, in the insulating body 31, communicating With said recess 36. The steel ball also serves as a bearing on which the cup and disc can pivot so as to be capable of universal movement with respect to the end face 34. Each chamber 40 houses a helical compression spring 41, upon one end of which the steel ball 39 bears when the aluminum cup is in position in the recess 36. A small brass cup, 42, is spigoted into the end of each spring 41 which is remote from the carbon disc assembly, and the recess 43 in said cup serves to locate a screw, 44, which is xed by means of a screwhead 45.

One or more brass discs, 46 (three are shown in the drawing), are located in that end of the driving component which contains the screws 44, said discs extending to the exterior of the insulating body 31, so that their peripheries form slip-rings on the exterior of the component; the brass ldiscs are insulated from one another by portions of the insulating body 3l. Each of the discs 46 is provided with six equally spaced holes, located in such positions that each of the six screws 44 will pass through a hole in each disc: the holes in each disc consist of four clearance holes, 47, through which four of the screws 44 pass without coming into contact with the disc, and two smaller, screw-threaded holes, 48, with which two of the screws 44 co-operate, the two screw-threaded holes in each disc being located diametrically opposite to one another with respect to the circumference of the disc. Electrically conducting connection of the conducting backing layer, 37, of each carbon disc, 35, to a slip-ring (that is to say to the periphery of one of the brass discs 46) is thus provided through the conducting adhesive and the aluminum cup 38, the steel ball 39, spring 41, brass cup 42, and screw 44 co-operating with the appropriate brass disc 46. For three-phase operation of the clutch, two diametrically opposed carbon discs are connected in this way to each slip-ring, and each slip-ring is arranged to be connected to one phase line conductor by means of a brush, in known manner.

One preferred method of preparing the carbon discs 35, employed in the driving component described above, comprises beating hemicellulosic pulp in water, the concentration of the pulp being 2% by weight, for four hours in a standard type of beater of the kind used in the paper-making industry, regenerating the hemicellulosic material by centrifuging the aqueous dispersion to remove the free water therefrom, pressing the centrifuged pulp in the form of discs, drying the discs and finally heating them to 500 C. in nitrogen under a pressure of about 30() atmospheres. The surfaces of the discs which are arranged to engage with the surface of the driven component in operation of the clutch are subjected to a suitable polishing treatment for imparting the required degree of smoothness to the surfaces.

The driven component of the clutch, shown in FIG- URE 1 of the drawings, comprises a plate, 49, of steel composed'of O.27-0.35% carbon, 0.5% manganese, 0.1-

0,35% silicon, 0.05% lead, 2.3-2.5 nickel,V (lA-0.7% molybdenum, 0.5-0.8% chromium, and the balance iron, this plate being mounted on a shaft 50. In a modification,

i not shown'in'the drawing, the steel plate may be thinner and may be mounted on a light alloy hub which is in turn mounted on a shaft. p

The construction of the driving component of the clutch of the form shown in FIGURES 1 and 2 of the drawings has been described with particular reference to the method of operating the clutch from-a three-phase star-connected Y alternating current supply: thus for this moderof operation, one diametrically opposed pair of carbon discs is connected VtoV each of three slip-rings 46, and each slipring is connected to one of the phase line conductors. However, a clutch of this form can, alternatively, be

operated from a direct current supply or from a single phase alternating current supply: in either of these cases Y Vthe six carbon discs, 35, are all arranged to be connected to a single supplyV conductor by means of a common conply is a balanced polyphase system, for example a'starfY connected system, theV plate 49 may be earthed. In the fcase ofA direct current operation,rthe steel plater49 is Vconnected to the positiveV pole, and the carbon discs V,are

connected to Ythe negative pole, of the supply. The steel plate 49 may'itself be directly connected to the supply,ror

if desired the Vdriven component kmay be provided with a slip-ring for connection tothe supply.

In the operation of a clutchY of the'form shown in FIG- Y .Y URES 1 and 2,7the Johnsen-Rahbek forceV required for Ycausing the carbon discs to engage with the steel plate 49 is developed in one micro-second after theapplication of a VsuitableV voltage, and the driven component is then accelerated to the'operatingjspeed in 50 to V60 microseconds'. Y

The results of tests which we havecarried out on a clutch of the form described above with reference to FIG- URES 1 and 2 of the drawings, when operated from direct current, single phase alternating current, and star-connected three-phase alternating Vcurrent supplies, respectively, areshown in the following table. In the particular clutch used for the tests, the six carbon discs were each 24 mm@ in diameter and 0.5 mm. in thicknessyand the exposed carbon surfaces of the individual discs wereV lapped with 600 grade Carborundum priorY to assembly of Y Vthe driving component `of the clutch, final polishing of the Vsaid surfaces Vof the discs being achieved by allowing the i clutch to operate under controlled slip conditionst torque is-the load at which the clutch willv repeatedlyY engage whenthere is 100% slip between V.the components;

the frictional drag is the Ytorque produced by fctional effects between the Vmutually engageableV surfaces Vof the clutch when Ythe clutch isV electrically de`energizedgQthe drive to drag ratio isV the ratio Yof the` running Vtorque transmitted to the frictional drag, the average figure for Y i the frictional drag being Vused in this case; and the control ratio is the ratio of the power (in Watts) transmitted through the clutch to therpower unit. Y

FIGURE 3 shows, in elevation, the end face 34 of the driving component of a clutch of the same form as that described above with reference to FIGURES 1 and 2, Y

modied in that the engageable surface of this component is formed in six separately mounted sections, 51,'each in the shape of a sector of .a circle, and all of thegsame dimensions and equally spaced around the face v34. The surface sections 51 are formed of semiconductive carbon manufactured by a process similar to that described above with reference to the discs 35 shown in FIGURES 1 and 2; in this case the regenerated hemicellulosic Lpulp is pressed in the form of a sheet, the sheet is dried,V andV Y portions Yof the requiredrshape of the sections 51, but somewhat larger to allow for shrinkage during thersubsequent heating, are cut from the dried sheet and are then heated to etect the required degree of carbonisation.

The manner of mounting theecarbon sections 51 on the* ,driving componentV is not'shown inFIGURE 3, but is similar to the manner of mounting the discs 35 shown in FIGURE 2. Thus the carbon sections 51 are mounted inV recesses inthe end face 34, each section' 51 being backed with silverY and fixed in an aluminium cup 52 of shape corresponding to that of the carbonV section,` andthe err-V 'Y terior surface .of each aluminiumV cup is fixed-to a steel ball for locating Vthe cup and carbon section in a chamber in the clutch component and forl imparting universal piv- .Y Y otalm'ovementrto the section.

In all other'Y respects the Vconstruction and manner of operation of the clutch provided with carbon surface sections of the form shown in FIGURE 3 are similar to those described above with reference to FIGURES 1 and'Z.

The rapid engagement of the engageable surfaces of the components, and the reduction in theV amount of slip occurring betweensaid Vsurfaces when engaged, Vachieved by the construction of a clutch component with a plurality of individually mounted surface sections, accordance Vwith the invention, render this construction particularly advantageous for use, not only in a Vclutch for operation as described above, but also in an electrostatic braking v mechanism. Thus VaV clutch construction of the kind described herein can readily be adapted for brake operationV by arranging that one ofthe componentsY is fixed in the stationary condition, the other component being capable of rotation or other motion, such as reciprocating motion,

55 relative to the stationary component, so that on engage-V TABLE Torque, lbs-inch, at 700 r.p.m. Y

' Drive to Slip angle, Y Power trans- Supply voltage Y drag degrees per Current used and Y mitted, brake Control Running On load Frictional ratio, revolution power input horse power ratio torque starting drag avg. j

` torque 32. 0 16.0 1.5 to 2.5-. 16:1 0.3 18 milliamps, 4.5 Watts. 0. 34 58:1 390 D.C 38.0 15. 5 do 19:1 (l) Y 35 milliamps, 13 Watts 0.4 22:1 4l5three-phase A. 26. 0 13. S 13:1 Y 0. 12 8 milliamps, 5.5 Watts- Y Y 0. 27 42:1 240 single phase A. 22. 0 1l. 11:1 0. 8 21 milliamps, 5 Watt-s.. 0:23 36:1

' 1 Net detectable.

The slip angleV (as hereinbefore defined) referred to in the table was measured at a torque of 20 lbs. inch in each case. Of the remaining termsemployed in the column headings of the table, the running torque is thertorque Y transmitted when the clutch components are engaged, and

is measured by dynamometer at the threshold of slip after the gradual application of the load; the on load starting yment of the mutually engageable surfacesof the two components, as a result of the application of a voltagerbetweenVV Y the components, the motion of the movable component is ponent has the electrically conducting surface member, and which the semiconductive surface member.

The present invention includes within its scope clutch arrangements consisting of, in combination, two or more electrostatic clutches of the kind specified, wherein one engageable surface member of each clutch of the combination is formed in a plurality of sections in accordance with the invention. In such an arrangement, one component may form part of two clutches, each face of said component being engageable with another component of the arrangement.

In one particular application of the invention, a clutch mechanism and a brake mechanism can be combined in a single arrangement. Such an arrangement comprises three components, namely a driving component, a stationary component, and, located between these two components, an intermediate component which is arranged to engage alternatively with the driving component and the stationary component, for imparting motion to the intermediate component and for braking such motion, respectively.

A clutch-and-brake arrangement of the last-described kind is shown diagrammatically in FIGURE 4 of the accompanying drawings. This arrangement consists essentially of a rotatable driving component 53 carried on a shaft 54 connected to a power source (not shown) by which the clutch is driven, a stationary braking component 55, and an intermediate component 56 which is capable of engaging with either the driving component 53 or the braking component 55, as desired, the intermediate component 56 being mounted on a shaft 57 for connection to a mechanism to be operated by means of the clutch-and-brake arrangement: the shaft 57 passes through an aperture in the stationary component 55.

The engageable surface members, 58 and 59, of the driving component and the braking component respectively, are both formed of metal, and both faces, 60 and 61, of the main body of the intermediate component 56 are provided with sectional surface members in accordance with the invention, the sections being formed of semiconductive carbon and being mounted on the main body of the component in a manner similar to that described above with reference to FIGURES 1 and 2. These sections may be of any desired shape, but are shown in the drawing in the form of discs, 62 and 63, mounted ou the main body faces 6d and 61 respectively, the respective sets of discs on the two surfaces being mounted out of alignment with one another, as shown (only two discs of each set are shown, for clarity), to facilitate accommodation of the mounting arrangements and electrical conductors, associated with the discs, within the main body of the component 56.

For operation of the clutch-and-brake system shown in FiGURE 4, electrical conductors provided on and within the component 56, and connected respectively to the sets of carbon discs 62 and 63, are also connected respectively to two terminals, 64 and 65, which can be alternatively connected to a source of electric current supply by means of a switch 66. Suitable connections are also made to the driving component 53 and the braking component 55, so that when the terminal 64 is connected to the supply by means of the switch 66 a voltage is applied between the engageable surfaces 58 and 62, and the component 56 is engaged with the driving component 53 and the motion of the latter is imparted to the intermediate component 56; and when the terminal 65 is connected to the supply by changing over the switch 66 a voltage is applied between the engageable surfaces 59 and 63, and the intermediate component 56 is engaged with the stationary component 55 to effect braking action on the component 56. As shown in the drawing, the system is arranged to be operated from a direct current supply, the components 53 and 55 being earthed. However, the system may alternatively be operated from a single phase or polyphase alternating current supply: in the case of a three-phase supply, for example, each of the engageable l@ surface members 62 and 63 consists of siX discs, the arrangements for mounting and lconnecting each set of discs being similar to those shown in FIGURE 2.

We claim:

1. An electrostatic clutch of the kind (A) operated by means of an electrostatic attraction produced between a surface of an electrically conducting member and a closely adjacent surface of a semiconductive member when a voltage is applied between the said members (I) which voltage is sufficiently high to produce a said electrostatic attraction of such magnitude as to cause adhesion between the said surfaces, and

(B) said clutch comprising two components each of which comprises a main body having a surface member directly engageable with a surface member of the other component, the said surface members being `composed respectively of an electrically conducting material and a semiconductive material,

(I) which components are capable of relative motion when the said mutually engageable surface members are disengaged, in the absence of a said applied voltage, the said surface members being in slipping Contact with one another when disengaged, and

(Il) between which components there is substantially no relative motion when the said mutually engageable surface members are engaged as a result of the application of a said voltage;

(C) wherein the said engageable surface member of a first said clutch component consists of a plurality of separate sections (I) each individually mounted on a ball bearing located in a recess in the main `body of the said component so as to be capable of universal pivotal movement relative to said main body,

(a) whereby, when the said mutually engageable surface members are in the disengaged position and in slipping contact, each said individually mounted section is automatically aligned With, so as to be wholly in close interfacial contact with, the engageable surface member of the second of said clutch components,

(i) for enabling engagement between each section of the engageable surface member of said first clutch component and the engageable surface member of said second clutch component to take place rapidly on the application of a said voltage between the said members.

2. A clutch according to claim 1, wherein each said ball bearing on which a said section is mounted is supported on one end of a compression spring which is retained in a chamber within the main body of the said component, which chamber opens out into said recess.

3. A clutch according to claim 1, wherein the said individually mounted sections are insulated from one another and wherein, for operation of the clutch from a polyphase alternating current supply, the main body of the clutch component of which the said sections form the engageable surface member carries conductors for connecting said sections separately to the respective supply conductors from the different phase circuits, at least one said section being provided for connection to each phase circuit.

4. A clutch according to claim 3, wherein at least two said sections are provided for connection to each phase circuit, and the sections to be connected to any one phase are symmetrically spaced apart upon the said surface of the main body of the clutch component of which the sections form the engageable surface member.

c 5. Arclutch according torclaim 1, wherein the individually mounted engageable surface member Vsections are ofY plane circular form.Y Y

6. A clutch according to claim 1, wherein the individually mounted engageable surfacermember sections are in the form of sectors of a circle. Y

7. A clutch according to claim 1, wherein the material employed for the construction of the semiconductive engageable surface member is semiconductive carbon cornposed of a partially carbonised regenerated material which is a member of the group consisting of cellulosic and hernicellulosic materials.

8. A clutch according to claim 7, wherein the individually mounted engageable surface member sections are formed of the said semiconductive carbon.

'References Cited t UNITED STATES PATENTS 2,850,907 9/1958Y Foster 192-84 2,924,314 2/ 1960 Shepard 192--18V 3,240,306 3/1966 Armstrong 192-84 MARK M. NEWMAN, Primary Examiner.

ARTHUR T. MCKEON, Examiner. 

1. AN ELECTROSTATIC CLUTCH OF THE KIND (A) OPERATED BY MEANS OF AN ELECTROSTATIC ATTRACTION PRODUCED BETWEEN A SURFACE OF AN ELECTRICALLY CONDUCTING MEMBER A CLOSELY ADJACENT SURFACE OF A SEMICONDUCTIVE MEMBER WHEN A VOLTAGE IS APPLIED BETWEEN THE SAID MEMBERS (1) WHICH VOLTAGE IS SUFFICIENTLY HIGH TO PRODUCE A SAID ELECTROSTATIC ATTRACTION OF SUCH MAGNITUDE AS TO CAUSE ADHESION BETWEEN THE SAID SURFACES, AND (B) SAID CLUTCH COMPRISING TWO COMPONENTS EACH OF WHICH COMPRISES A MAIN BODY HAVING A SURFACE MEMBER DIRECTLY ENGAGEABLE WITH A SURFACE MEMBER OF THE OTHER COMPONENT, THE SAID SURFACE MEMBERS BEING COMPOSED RESPECTIVELY OF AN ELECTRICALLY CONDUCTING MATERIAL AND A SEMICONDUCTIVE MATERIAL, (I) WHICH COMPONENTS ARE CAPABLE OF RELATIVE MOTION WHEN THE SAID MUTUALLY ENGAGEABLE SURFACE MEMBERS ARE DISENGAGED, IN THE ABSENCE OF A SAID APPLIED VOLTAGE, THE SAID SURFACE MEMBERS BEING IN SLIPPING CONTACT WITH ONE ANOTHER WHEN DISENGAGED, AND (H) BETWEEN WHICH COMPONENTS THERE IS SUBSTANTIALLY NO RELATIVE MOTION WHEN THE SAID MUTUALLY ENGAGEABLE SURFACE MEMBERS ARE ENGAGED AS A RESULT OF THE APPLICATION OF A SAID VOLTAGE; (C) WHEREIN THE SAID ENGAGEABLE SURFACE MEMBER OF A FIRST SAID CLUTCH COMPONENT CONSISTS OF A PLURALITY OF SEPARATE SECTIONS (1) EACH INDIVIDUALLY MOUNTED ON A BALL BEARING LOCATED IN A RECESS IN THE MAIN BODY OF THE SAID COMPONENT SO AS TO BE CAPABLE OF UNIVERSAL PIVOTAL MOVEMENT RELATIVE TO SAID MAIN BODY, (A) WHEREBY, WHEN THE SAID MUTUALLY ENGAGEABLE SURFACE MEMBERS IN THE DISENGAGED INDIVIDUALLY MOUNTED SECTION IN AUTOMATICALLY ALIGNED WITH, SO AS TO BE WHOLLY IN CLOSE INTERFACIAL CONTACT WITH, THE ENGAGEABLE SURFACE MEMBER OF THE SECOND OF SAID CLUTCH COMPONENTS, (1) FOR ENABLING ENGAGEMENT BETWEEN EACH SECTION OF THE ENGAGEABLE SURFACE MEMBER OF SAID FIRST CLUTCH COMPONENT AND THE ENGAGEABLE SURFACE MEMBER OF SAID SECOND CLUTCH COMPONENT TO TAKE PLACE RAPIDLY ON THE APPLICATION OF A SAID VOLTAGE BETWEEN THE SAID MEMBERS. 